ST-segment elevation myocardial infarction (STEMI) is a transmural infarction caused by a total occlusion in the coronary flow where mechanical reperfusion therapy with primary percutaneous coronary intervention (PCI) is initially recommended. The STEMI can decrease left ventricular compliance, resulting in diastolic dysfunction, which can cause an increase in left ventricular end-diastolic pressure (LVEDP) in the early stages. Prolonged reperfusion time has been associated with increased LVEDP, although the mechanism remains unclear. This research aims to determine the correlation between reperfusion time and LVEDP in STEMI undergoing primary PCI. Research Methods This research is Analytic observational with a cross-sectional study conducted at RSUP dr. Sardjito in September-October 2022. The population was all STEMI patients undergoing primary PCI. The data included demographic profile, comorbidities, coronary profile, and reperfusion time. The invasive procedure took the value of LVEDP in the cath lab after primary PCI. Results found From 31 patients who met the inclusion and exclusion criteria, the median reperfusion time was 170 minutes (120-6360 minutes), and the median LVEDP was 20 mmHg (10-32 mmHg). In correlation analysis with Spearman, there was a significant correlation between reperfusion time and LVEDP (p=0.001) with a strong correlation coefficient (r=0.630). In multivariate analysis, there were variables with a significant relationship to LVEDP, including age (p=0.001; r=0.147) and IRA (p=0.001; r=4.080). There is a significant correlation between reperfusion time and LVEDP in STEMI undergoing primary PCI.